Ultra high frequency device



Jan. 7, 1941. R M SMITH 2,227,604

ULTRA `HIGH FREQUENCY DEVICE Filed Jan. 29, '1938 2 Sheets-Sheet l E: L O

l; 1G. @3.1. 115 Fr W M :inventor l R0 `ere; M. S'mith Ctttorneg Jan. 7, 1941. R M, SMITH I 2,227,604

ULTRA HIGH FREQUENCY DEVICE Rage r6' M Smith,

Patented Jan. 7, 1941 UNITED STATES ULTRA HIGH FREQUENCY DEVCE Rogers M. Smith, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 29, 1933, Serial No. 187,607

8 Claims.

My invention relates to ultra high frequency devices, and especially to means for tuning ultra high frequency devices whereby undesired reactances may be neutralized. Reference is made to my copending application Serial No. 293,624, filed September 6, 1939 for Ultra high frequency devices, said application being a division of the instant application.

In radio circuits operated at frequencies up to 10 thirty megacycles per second the capacitors and inductors used for tuning are usually of the lumped or concentrated type. For example, conventional electrical condensers and solenoid types of inductors are used from the lowest radio frequencies and up to frequencies of the order of thirty megacycles per second. At frequencies appreaching ve hundred megacycles per second and upward transmission lines of the two wire or concentric type are used as resonant circuits.

2O When transmission lines and associated thermionic tubes are used at ultra high frequencies, the input impedance of the tubes has an impor.- tant effect on the results obtainable. It is well known that the electrons moving from cathode to anode through the grid electrode of a thermionic tube, while of slight or negligible effect at low frequency, cause a very substantial reduction of input impedance at the ultra high frequencies. The natural capacity between the cathode and grid electrodes, as well as electrode leads having appreciable length, while effecting slight reactance at low frequencies, offer large reactive effects at the ultra high frequencies.

The net effect of the input resistance and input reactance of thermionic tubes operated at the ultra high frequencies is to establish phase shifts which are often large enough to have adverse effects on the tubes as amplifiers. I have found that similar effects in the anode or output circuits account for an actual attenuation of signal frequency currents instead of an expected gain. These effects may be overcome by suitable tuning adjustments, provided the tuning elements are designed so that the connecting leads offer negligible reactance.

In practice a real problem is presented in the elimination of the effects of connecting leads. One might assume that a capacitor could a1- ways be connected to by-pass the ultra high frequency currents. However, the use of a by-pass capacitor usually simply shifts the problem from the original leads to the leads of the capacitor itself. The importance of the lead lengths at ve hundred megacycles per second can be illustrated by stating that a grounded lead fifteen (Cl. NSL-171) centimeters long standing in space will have minimum impedance at the grounded end and maximum impedance at the free end. Obviously, intermediate lead lengths will have intermediate impedances.

My invention has for one of its objects the provision of means for eliminating the effects of lead lengths in ultra high frequency circuits. Another obiect is to provide means for eliminating the reactive effects of the interelectrode capaci- 10 ties within a thermionic tube. Another object is to provide means for tuning the transmission lines associated with ultra high frequency thermionic tubes. An additional object is to provide means for efficiently converting currents of ultra 15 high frequency to currents of intermediate frequency. A further object is to provide means for preventing sustained blocking of an ultra high frequency receiver by the application of signals of large amplitude.

My invention is described by reference to the accompanying drawings in which Figure 1 is a schematic circuit diagram of a radio frequency amplifier, local oscillator and first detector;

Figure 2 is a sectional view of one embodiment of my invention; and

Figure 3 is a sectional view of an oscillator which may be used in conjunction with the ap- 3 paratus of Fig. 2.

Referring to Fig. l, which is a diagrammatic circuit used for purposes of illustration only, a transmission line I is connected by a matching transformer 3 to the input of a thermionic amplifer 5. The input circuit of the amplifier includes a resistor I and a capacitor 9 which prevent overloading or blocking on application of signal currents of large amplitude. The output circuit of the amplier includes an adjustable in- 40 ductor II, a bypass capacitor I3 and a coupling capacitor I5.

The coupling capacitor I5 is connected to a pair of resonant coupled circuits I1, I9 which are grounded. The second resonant circuit I9 is 45 mutually coupled to a local oscillator 2|. The second resonant circuit is also connected to a first detector or mixing tube 23. The input of the detector includes an adjustable inductor 25. The output of the first detector includes a network 50 2l which is preferably tuned to intermediate frequency currents and which is connected to an intermediate frequency amplifier and second detector. The intermediate frequency amplifier and second detector are not illustrated because they 55 are not essential parts of my invention and they are well known to those skilled in the art.

It should be understood that the thermionic tubes of the foregoing circuit are energized by application of suitable anode, screen, and heater currents. Likewise, the grid electrodes may be biased negatively with respect to cathodes by selfbiasing means, biasing batteries or the like. Bypass capacitors are shown as applied in the conventional manner. While the schematic diagram shows the inductors, and capacitors as conventional elements, such showing -is for the purpose of illustration only.

For the practical application of my invention reference is made to Fig. 2 in which the line 29 represents the inner conductor of a concentric transmission line, which is terminated by a coupling or matching transformer 3| of the concentric line type. The inner conductor 33 is inductively coupled to the grid connection 35 of the radio frequency amplier 31 and is terminated by grounding on the outer conductor of the transformer. The input circuit to the amplifier 31, which includes the leads and electrodes within the thermionic tube, is arranged as follows: The amplier tube is mounted on a plate 39 which is located within a metal housing 4|. A metal tubular member 43 is adjustably mounted within a boss 45 in the housing. The tubular member may be capped by an insulated plug 41. At the lower end of the tubular member a bypass capacitor is formed by insulating, with Styrol or the like, a metal plug 49 from the tubular member.

the circuit between the grid electrode and the bypass capacitor formed by 49, etc. The inductive reactance of this circuit is adjusted to substantially neutralize the capacitive vreactance of the ampliiier input. It should be recognized that the leads and electrodes within the amplifier are a part of the resonant circuit. It will be observed that the capacitance of the bypass capacitor remains fixed. To insure that the junction of the bypass capacitor and the housing shall be grounded at a point of suitable impedance, the

rod 35 is concentrically extended within the tubular member 43 and terminated by a sliding concentric tube 51. This supplemental grounding circuit is required because of the relatively small capacity of the bypass condenser.

If the ground connection is to be made of low impedance, the slidable tube 51 is adjusted so that the rod 53 and tube 51 have an effective length of one quarter wave measured from the ground point toward the high potential end of The balance of .the amplier input circuit corresponds to the transformer 3 of Fig. 1.

Ihe output circuit of the amplier 31 is as follows: 'Ihe anode is connected to a plate 59 which is separated by an insulator 6| from a quarter wave -line hereinafter described. The anode is also connected, through a conductor 63 of adjustable length, to the positive terminal of a B-battery. 'I'he upper portion of the conductor 63 is slidable with respect to a metal plug 61, which is separated from an outer tubular member 69 by a suitable insulator 1|, such as Styrol. The plug B1, the insulator 1| and .the tubular member 69 form a bypass capacitor, which is adjustably mounted in a grounded member 13. This bypass condenser may have a large capacity because the problem of blocking does not present itself in the anode circuit. Also no supplemental ground circuit is required because the capacity may be made sufficiently large to eiectively bypass. If, however, the capacity for `any reason is to be kept low, the structure described in connection with the amplier input circuit may be used.

The eective length of the conductor $3 is adjusted by moving the tubular member 69 back and forth within the member 13. The bypass capacitor formed with .the tubular member 69 is fixed in its capacitance, has for practical purposes no leads, and directly and eiectively forms a bypass from the conductor 63 to ground. Thus, the effective length of the anode circuit may be adjusted to neutralize capacity reactance with the amplier 31. The conductor 63 and the bypass capacitor 61, 1|, 69 correspond to the inductor and the capacitor 3, respectively, of Fig. 1.

The coupling between the ampliier output circuit and the input to .the detector 15 is a pair of quarter wave concentric lines 11, 19, which are connected together and are grounded at their junction by a screw 8|. The screw 8| acts as the common coupling between the two quarter wave circuits. In some arrangements, a single quarter wave line may be made common to both circuits, acting, for example, as an autotransformer. The inner conductor 33 of the concentric lines may be positioned within the outer conductor by an insulated support 81. The lower 11 and upper 19 quarter wave lines may be tuned by trimmer capacitors 89, 9|. The amplier is coupled to the lower line 11 by the capacitor formed by the plate 59 and insulator 6| which may be fastened to the inner conductor 83 as shown. The input to the rst detector 15 is made by connecting the grid lead 93 to ythe inner conductor 83 at a point of suitable impedance match. The input tuning may be adjusted by means similar to that shown for the input of amplifier 31 or by suitably choosing the length 4of a conductor 95 connected from the grid to the outer conductor 85. The former means is preferred if excessive overloading or blocking eiects are present in the detector. The quarter wave lines 11, 19 and the conductor 95 are equivalent, respectively, to the circuits |1, |9 and the inductor 25 of Fig. 1.

The local oscillator 91 is coupled to the detector input circuit by adjusting the mutual coupling between the inner conductor 99 of the oscillator and the upper quarter wave line 19. The outer conductor IUI of the oscillator is slidably mounted on .the conductor 85 and spaced therefrom by an insulating sleeve |93. The insulation is necessary in the instant arrangement because the outer conductor |9| is at oscillator anode potential while the conductor 85 is at ground potential.

A suitable construction for the oscillator is shown in Fig. 3. The inner and outer conductors 99 and lill and the insulating sleeve |03 correspond to the fragmentary showing in Iiig. 2. The outer conductor lill is divided by a ground plate i535. The inner conductor 99 is suitably fastened, by soldering, brazing, threading or the like, to the ground plate. The oscillator tube itl is fastened to a socket HB9 or the like which may be supported within the conductor lill. The grid electrode is coupled to the ground plate through a capacitor lill. The anode is connected by a lead ill to the inner conductor @i9 `at a point of suitable impedance. The cathode is coupled to the inner conductor through lead ii3 and a capacitor IM. The oscillator frequency may be adjusted over a small frequency range by a trimmer plate H5 located near the anode lead lll. This trimmer capacitor, and the quarter Wave line trimmers B9, 9| have capacities which are very small compared to the total capacity of the associated lines, whereby the desirable characteristics of the concentric lines are retained.

Thus I have described an ultra high frequency device in which the input and output reactances of the associated thermionic tubes may be neutralized by adjustable elements of opposite reactance. Where the by-passing is critical, the capacitors have no leads of appreciable length. Means are disclosed for establishing points of high or low impedance as may be required. The arrangement shown is further characterized by the relative disposition of the component parts which are positioned to reduce the lengths of leads to a minimum. Finally, the component parts are largely concentric lines in which the losses are extremely low, temperature effects may be corrected, high frequency stability may be obtained and other desirable features, known to those skilled in the art, are present. It will be obvious that my invention may be applied to ultra high frequency transmitting and receiving devices. I have chosen to describe the latter merely by way of illustration.

I claim as my invention:

l. In an ultra high frequency amplifier, a thermionic tube having input connections and output connections, means for tuning said input connections, said input tuning means including a fixed conductor having a reactive component and a conductor adjustable with respect to said fixed conductor, said input connections including a low potential point and a high potential point, said fixed conductor being effectively connected to one of said points, said adjustable conductor being effectively connected to the other of said points, a capacitor, said capacitor including a plug slidably connected to said xed conductor and at least a portion of said adjustable conductor as its respective plates and a dielectric portion movable with the said portion of said adjustable conductor, and a tunable circuit effectively connected to said plates for supplementing the path across said capacitor Whereby a low impedance path to ground is established.

2. In a device of the character of claim 1, a resistor connected between said capacitor elements and slidable therewith.

3. In a device of the character of claim l, said output tuning means including a reactive conductor and a capacitor having one element slidably connected thereto, and having its other element slidably connected to ground.

4. In an ultra high frequency amplifier, a thermionic tube having input and output connections, said input connection including a rod, a plug slidable on said. rod, a metal tube, insulating means for securing said plug Within said metal tube, avbushing within which said metal tube is slidably mounted, and means for grounding said input circuit and said metal tube at said mounting, whereby the effective length of said rod may be varied and said input connection tuned.

5. In a device of the character of claim 4, said output connection including a rod, a plug slidable on said rod, a metal tube, insulating means for securing said plug within said metal tube, a bushing within which said metal tube is slidably mounted, and means for grounding said bushing, whereby the effective length of said rod may be varied.

6. In an ultra high frequency amplifier, a thermionic tube having input connections and output connections, means for tuning said input connections, said input tuning means including a fixed conductor having a reactive component and a conductor adjustable with respect to said fixed conductor, said input connections including a low potential point and a high potential point, said Xed conductor being eectively connected to one of said points, said adjustable conductor being effectively connected to the other 0f said points, a capacitor, said capacitor including a plug slidably connected to said fixed conductor and at least a portion of said adjustable conductor as its respective -plates and a dielectric portion movable with the said portion of said adjustable conductor, and a tunable concentric line connected to said fixed and adjustable conductors supplementing the path across said capacitor.

7. In an ultra high frequency device, a thermionic tube having a reactive circuit, and means for neutralizing said reactive circuit including a conductor having a reactive component opposite in sign to the reactive component of said circuit connected to the high potential point of said circuit and effectively connected to a low potential point by a capacitor having a slidable contact on said conductor and a second contact slidable with respect to said low potential point, and a tunable line connected across said capaci- CID tor to supplement said capacitor and insure a low impedance path from said conductor to said low potential point.

8. In an ultra high frequency device, a thermicnic tube having a reactive circuit having high and low potential terminals, and means for neutralizing said reactive circuit including a conductor having a reactive component of the opposite sign to the reactive component of said circuit and having one portion connected to said high potential terminal and another portion which is effectively connected to said low potential terminal by a capacitor having two conductive elements, one element being slidably connected to said first mentioned conductor, the other element being slidably connected to said low potential terminal, and a tunable transmission lin-e connected across said capacitor to supplement said capacitor and insure a low impedance path from said conductor to said low potential terminal.

ROGERS M. SMITH. 

